Wind instruments (technical name: aerophones) A. Brass instruments The players lips vibrate against each other and against the rim of a cup mouthpiece.

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Presentation on theme: "Wind instruments (technical name: aerophones) A. Brass instruments The players lips vibrate against each other and against the rim of a cup mouthpiece."— Presentation transcript:

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Wind instruments (technical name: aerophones) A. Brass instruments The players lips vibrate against each other and against the rim of a cup mouthpiece. Lips act as a valve, introducing puffs of air at just the right time to maintain oscillations of the air column Note that an instrument is classified as brass not because it is made of metal, but because it has this type of mouthpiece, which relies on vibrating lips. B. Woodwind instruments The player blows air against a sharp edge or through a reed The sound vibration usually begins at the mouthpiece. The rest of the instrument magnifies, and turns this vibration into a pretty sound Wind instruments are classified by mouthpiece types: 1

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Acoustic Impedance curve Acoustic impedance is a function of frequency Acoustic impedance curves have peaks at resonance frequencies Role of acoustic impedance in brass instruments At the frequencies of impedance peaks the excess pressure helps to open the lips (pressure cooperates with the lips) – regenerative or positive feedback 5

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The bell All brass instrument have bells Bell changes spectrum of the radiated sound Bell changes acoustic impedance curve (both the frequencies and heights of the resonance peaks) Bell changes the radiation pattern, making it more directional at high frequencies (Why at high frequencies?) It allows more efficient radiation of sound by matching the high pressure inside the horn with the lower pressure outside The mouthpiece It shifts the frequencies of the impedance peaks, but has more dramatic effect on peak heights, especially enhancing low resonances. Popping frequency – the lowest resonance of a brass instrument mouthpiece (750-850 Hz) Question: Estimate the length of the mouthpiece. 7

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http://cnx.org/content/m12364/latest/trumpetvalve.swf Valves Valves are more commonly found on brass instruments. Pressing a valve makes the air flow through an extra section of tube, temporarily making the instrument longer in between the mouthpiece and the bell. The slightly longer instrument gets a slightly lower fundamental harmonic, and a lower harmonic series. (A few valves are ascending valves, which cut off a section of tubing and so raise the pitch.) animation Slides (trombone) Seven positions of the slide are needed to play all desired notes of the scale These positions are not equally spaced (for a semitone down ~6% elongation) Problems with valves position and slides length 8